It has become standard in recent years to equip most types of mobile devices, such as mobile telephones, with cameras for capturing still images and/or video. Due to a demand for high quality images, the cameras are becoming more sophisticated and generally comprise a lens system with an autofocus mechanism to automatically perform a focusing operation.
Among existing autofocus mechanisms, some are termed “passive” autofocus systems, which generally involve processing images captured by the image sensor to detect when focusing has been achieved, for example by performing contrast or phase detection. Other autofocus mechanisms, termed “active” autofocus systems, rely on a dedicated ranging device to estimate the distance to an object in the image scene, allowing a rapid convergence to an appropriate lens position.
A drawback with passive autofocus mechanisms is that they tend to be relatively slow in providing the optimum lens position. However, while it would be desirable to rely solely on an active autofocus mechanism, in certain cases the ranging device is unable to provide a distance reading.
Hybrid autofocus systems use a combination of passive and active autofocus methods. If the active autofocus mechanism fails, the passive autofocus sequence is triggered to provide the autofocus function. Therefore, while such a hybrid system can provide a shorter focusing time using the active autofocus method, in the case that this method fails, focusing is still likely to be slow.
There is thus a need in the art for an autofocus method and system permitting faster focusing.